Most manufacturers of oriented strandboard (OSB) panels in North America use a common practice of bundling and packaging multiple panels into units in preparation for shipment to distributors, retailers and lumberyards. Units are composed of a stack of about 40 to 100 panels. Typically the individual panels are 4 feet wide, and 8 feet or 16 feet long. Individual panel thickness values range between 0.225 inch to 1.25 inches. Most units are between 3 to 4 feet in height and so the number of panels in a unit is largely determined by the thickness of the individual panels.
OSB units are typically subjected to a finishing process that generally includes the following three steps. First, units are transported into a booth where the four sides of the unit are sprayed with a liquid edge sealant, which dries to form a hydrophobic coating that helps to reduce edge thickness swell if the panels are exposed to rain at construction site. Quite often the liquid edge sealant is colored to visually differentiate the product in the marketplace. Then, the sealed unit is strapped to secure the bundle during shipping and storage. Finally, the sealed and strapped unit is labeled (e.g., stenciled) to designate the panel manufacturer, as well as the number, type and size of panels in the unit. Labeling is usually done in one of two ways. Units based on the most premium panels are often wrapped in a high-basis weight packaging paper that has a sophisticated, highly decorative label printed on the outside. The packaging paper serves a protective as well as a labeling function, and in some cases this combination of attributes has been worth the added cost. Most OSB units are not wrapped in packaging material, but are instead labeled with a relatively simple stencil and paint system.
In the stencil and paint labeling system, a stencil is placed against the side of a sealed and strapped OSB unit and paint is sprayed through the stencil onto the side of the unit. Generally the stencil is composed of steel or aluminum and is designed to create images of letters, numbers, and company logos or icons on the side of the unit. Some of these designs can be a bit intricate, especially around the letters and numbers. The metal around these intricate areas generally exists as narrow, strips, which are delicate and will bend or break with excessive mechanical stress.
Conventional labeling paint for an OSB finishing line, such as High-Hide White Stencil Paint, which is produced by Associated Chemists Inc. (ACI) [Portland, Oreg.], has a color that sharply contrasts with the color of the edge sealant. Effective contrasting color selection of the edge sealant and stencil paint provides a visually appealing, dramatic appearance to the unit.
Conventional labeling paints are designed to be very low in viscosity in order to improve the atomization properties of the paint at low spray pressure settings. Low spray pressure settings are generally used to minimize the amount of overspray that accumulates on the stencil. The low viscosity of conventional labeling paint makes it very prone to dripping. Accumulated overspray on the stencil often drips into some of the intricate stencil voids where it dries and occludes the opening. To cope with this dripping problem, operators on the OSB finishing line are generally forced to clean the stencil once every 20 to 25 minutes. In some cases operators apply heat to the stencil in an attempt to dry the accumulating paint before it has a chance to drip. Heating has marginally improved the dripping problems on some finishing lines, but it increases the complexity of the operation and it represents a bum hazard to the operators. Heating can also increase the strength of the bond between the paint and the metal as the paint dries. Unfortunately, conventional labeling paint forms a strong bond to the metal as it dries and operators must scrape with considerable force in order to remove it. Eventually, the harsh scraping action destroys the most delicate parts of the stencil.
Accordingly, there exists a need for a better labeling paint for an OSB finishing line. The ideal labeling paint has the following attributes.
Regulatory compliance: The labeling paint is water-based and should not contain any highly toxic or hazardous components.
Formulation stability: The labeling paint should not exhibit any phase separation or sediment formation during storage (the ACI labeling paint exhibits gross sediment formation unless it is frequently agitated).
Sprayability: The labeling paint is readily atomized in a spray system and should be resistant to nozzle clogging.
Bleed resistance with edge sealant: Usually, the edge sealant is still wet when the labeling paint is applied over it. Because these materials typically have sharply contrasting colors, it is important that they do not bleed into each other.
Ability to wet-out edge sealant: The edge sealant generally contains a high level of waxes and it becomes very hydrophobic as it dries. The labeling paint must wet-out the surface of the edge sealant and develop adequate bond strength to the edge sealant as it dries.
No dripping: The labeling paint should not drip into the openings (e.g., letters or numbers) on the stencil prior to drying.
Film Formation: The labeling paint should form a film as it dries and should not remain wet and sticky for very long subsequent to application.
Weak bond to metal stencil: The labeling paint must form a very weak bond to the metal stencil in order to ensure its easy removal from the stencil.
Appearance: The labeling paint should provide an image, symbol, or icon that is visually intense and saturated even when the labeling paint is used at low application rates.